The present invention relates generally to a quick-return electro-mechanical actuator, and, more particularly, to an improved tandem solenoid arrangement that is well suited for use in securing the cockpit door in a commercial aircraft and that offers the feature of quick return and release when it is desired to unlock the door.
A cockpit door lock solenoid is an electro-mechanical device designed for selectively locking and unlocking a commercial aircraft cockpit door. In addition to enabling a pilot to remotely lock and unlock the cockpit door for security reasons, such a door lock mechanism must be designed to unlock within three milliseconds when electronically triggered by a sensor detecting decompression in the cockpit and/or cabin. Otherwise, the differential pressure across the door may preclude the door from being opened.
Since the events of Sep. 11, 2001, cockpit door lock solenoids have been mandated on a wide variety of commercial aircraft to provide security to the cockpit.
It would be generally desirable to provide an improved quick-return electro-mechanical actuator that is distinguished from other solenoid-type mechanisms by a quick-return feature and by low-power consumption, which reduces the amount of generated heat, during continuous duty cycles.
Details of various prior art tandem-operated solenoids, albeit not necessarily applied to securing cockpit doors, are shown and described in one or more of the following U.S. Pat. Nos: 6,427,811, 4,639,700, 4,548,408, 4,366,564, 4,191,248, 4,103,120, 3,736,054 and 3,275,964.
Accordingly, it would be generally desirable to provide an improved electro-mechanical actuator that offers the capability of a long actuation stroke, a quick return upon the occurrence of a sensed-condition (e.g., cockpit and/or cabin depressurization, etc.), and reduced power consumption and reduced heat generation when held in a cocked position for a long period of time.
With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiment, merely for purposes of illustration and not by way of limitation, the present invention broadly provides an improved quick-return electro-mechanical actuator (20).
In one aspect, the improved actuator broadly includes a cocking solenoid (21) having a first body (23), a first armature (24) movably mounted on the first body, and a first coil (25) mounted on the first body and adapted to be selectively energized to cause the first armature to move between return and cocked positions; a first rod (26) movably mounted on the first body for movement with said first armature; a first spring (29) operatively arranged to urge the first rod and first armature to move toward such return position; a holding solenoid (22) having a second body (30), a second armature (31) movably mounted on the second body for movement between retracted and extended positions, and a second coil (32) mounted on the second body and adapted to be selectively energized to hold the second armature in its extended position; a second rod (33) mounted on the second body for movement with the second armature; a second spring (35) operatively arranged to urge the second rod and second armature to move toward the retracted position; and a control circuit (36) selectively operable to energize the first and second coils to move the first armature to its cocked position and to move the second armature to its extended position, and to de-energize the first coil when the second armature is held in its extended position; whereby, when the first coil is de-energized, the first spring may expand to move the first armature back toward its return position such that the mass of the second armature will be separated from the mass of the first armature so that when the second coil is subsequently de-energized, the second spring will expand to quickly move the second rod from its extended position toward its retracted position.
In another aspect, the invention provides a quick-return electro-mechanical actuator (20), comprising: an actuating member (33) having a range of motion between a retracted position and an extended position; a return spring (35) operatively arranged to urge the actuating member toward the retracted position; a cocking solenoid (21) selectively energizable to move the actuating member from its retracted position to its extended position; a unidirectional coupling (24,26,29) between the cocking solenoid and the actuating member for urging the cocking solenoid to separate from said actuating member when said cocking solenoid is de-energized so as to subsequently allow independent motion of the actuating member; and a holding solenoid (22) selectively energizable to hold the actuating member in the extended position after the cocking solenoid has been de-energized and the cocking solenoid has separated from the actuating member such that the return spring may quickly accelerate the actuating member from its extended position toward its retracted position without any further displacement of the cocking solenoid or the coupling when the holding solenoid is subsequently de-energized.
In the disclosed embodiment, the cocking and holding solenoids are structural different so as to adapt each to its stated function. The cocking and holding solenoids have magnetic circuits that are independent of one another. In other words, they have separate and non-overlapping paths of magnetic flux. The cocking solenoid may have a magnetic circuit (42) that includes a fixed-reluctance radial air gap (43xe2x80x2) and a variable-reluctance axial air gap (43) arranged in series with one anther. The axial air gap of the cocking solenoid may be defined between facing frusto-conical surfaces.
The holding solenoid may have a magnetic circuit (49) that includes two variable-reluctance axial air gaps (51,51) arranged in series with one another. The holding solenoid magnetic circuit may not include a fixed-reluctance radial air gap.
In the disclosed embodiment, the mass of the first armature is greater, and perhaps substantially greater, than the mass of the second armature. The spring rate of the second spring may be, and preferable is, substantially greater than the spring rate of the first spring.
The first body may have a surface that functions as a stop for movement of the first armature. The first spring may act against the first body, and the second spring may act against the second body.
In the preferred embodiment, the first and second rods are coaxial, although this need not variably obtain.
The holding solenoid is adapted to produce a holding force sufficiently high to hold the second armature against the second body so that the first coil may be thereafter de-energized. The second rod may be formed of a low-mass high-strength metallic material. A spacer may be positioned between the second armature and the second body to hold the second armature in spaced relation to the second body when the second armature is held in its extended position.
The control circuit may further include means (55) for delaying the decay of stored magnetic energy in the first solenoid. The first coil may be de-energized as a function of the position of the second rod relative to the second body.
Accordingly, the general object of the invention is to provide an improved quick-return electro-mechanical actuator.
Another object is to provide an improved solenoid mechanism in which a quick-return feature is a function of the low mass of a displaced armature, the high spring rate of a return spring, the presence of a spacer or shim between the second armature and second body, and the particular material of the second rod, all of which contribute to limit the exponential rise of the flux magnitude flux across the air gap as it approaches zero. These last two features permit the magnetic field produced by the second coil to collapse quickly when the second coil is de-energized.
Another object is to provide an improved actuator that is particularly suited for use in securing the cockpit door of a commercial aircraft.
Another object is to provide a cockpit door latching solenoid that offers the capability of a long stroke, and quick release in the event of a sensed-condition, such as cockpit and/or cabin depressurization.